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NFSv4                                                         C. Hellwig
Internet-Draft                                             June 04, 2017
Intended status: Informational
Expires: December 6, 2017


          Using the Parallel NFS (pNFS) SCSI Layout with NVMe
              draft-hellwig-nfsv4-scsi-layout-nvme-01.txt

Abstract

   This document explains how to use the Parallel Network File System
   (pNFS) SCSI Layout Type with transports using the NVMe or NVMe over
   Fabrics protocol.

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   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on December 6, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
     1.2.  General Definitions . . . . . . . . . . . . . . . . . . .   2
   2.  SCSI Layout mapping to NVMe . . . . . . . . . . . . . . . . .   3
     2.1.  Volume Identification . . . . . . . . . . . . . . . . . .   3
     2.2.  Client Fencing  . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Volatile write caches . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The pNFS Small Computer System Interface (SCSI) layout [RFC8154] is a
   layout type that allows NFS clients to directly perform I/O to block
   storage devices while bypassing the MDS.  It is specified by using
   concepts from the SCSI protocol family for the data path to the
   storage devices.  This documents explains how to access PCI Express,
   RDMA or Fibre Channel devices using the NVM Express protocol [NVME]
   using the SCSI layout type by leveraging the SCSI Translation
   Reference ([NVME-STLR]).  This document does not amend the pNFS SCSI
   layout document in any way, instead of explains how to map the SCSI
   constructs used in the pNFS SCSI layout document to NVMe concepts
   using the NVMe SCSI translation reference.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  General Definitions

   The following definitions are provided for the purpose of providing
   an appropriate context for the reader.

   Client  The "client" is the entity that accesses the NFS server's
      resources.  The client may be an application that contains the
      logic to access the NFS server directly.  The client may also be
      the traditional operating system client that provides remote file
      system services for a set of applications.

   Server  The "server" is the entity responsible for coordinating
      client access to a set of file systems and is identified by a
      server owner.



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2.  SCSI Layout mapping to NVMe

   The SCSI layout definition [RFC8154] only references few SCSI
   specific concepts directly.  This document uses the NVMe SCSI
   Translation Reference document ([NVME-STLR]) to provide mappings from
   these SCSI concepts to NVM Express ([NVME]) concepts that SHOULD be
   used when using the pNFS SCSI layout with NVMe devices.

   The NVMe SCSI Translation Reference is used to define the NVMe
   command and concepts that SHOULD be used to implement the pNFS SCSI
   layout.  Implementations MAY or MAY not use an actual SCSI to NVMe
   translation layer.

2.1.  Volume Identification

   The pNFS SCSI layout uses the Device Identification VPD page (page
   code 0x83) from [SPC4] to identify the devices used by a layout.
   Section 6.1.4 of [NVME-STLR] lists ways to build SCSI Device
   Identification descriptors from NVMe Identify data.  To be used as
   storage devices for the pNFS SCSI layout, NVMe devices MUST support
   either the EUI64 or NGUID value in the Identify Namespace data, as
   the methods based on the Serial Number for legacy devices might not
   be suitable for unique addressing needs and thus MUST NOT be used.
   If possible NVMe devices uses as storage devices for the pNFS SCSI
   layout SHOULD support the NGUID value as it is the larger identifier.

2.2.  Client Fencing

   The SCSI layout uses Persistent Reservations to provide client
   fencing.  For this both the MDS and the Clients have to register a
   key with the storage device, and the MDS has to create a reservation
   on the storage device.  Section 6.7 of [NVME-STLR] contains a full
   mapping of the required PERSISTENT RESERVE IN and PERSISTENT RESERVE
   OUT SCSI command to NVMe commands which SHOULD be used when using
   NVMe devices as storage devices for the pNFS SCSI layout.  One
   important difference between SCSI and NVMe Persistent Reservations is
   that NVMe reservation keys always apply to all controllers used by a
   host (as indicated by the NVMe HOSTID).  This behavior is somewhat
   similar to setting the ALL_TG_PT bit when registering a SCSI
   Reservation key, but actually guaranteed to work reliably.

2.3.  Volatile write caches

   The equivalent of the WCE bit in the Caching Mode Page in [SBC3] is
   the Write Cache Enable field in the NVMe Get Features command, see
   Section 6.3.3.2 of [NVME-STLR].  If a write cache is enable on a NVMe
   device used as a storage device for the pNFS SCSI layout, the MDS




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   must ensure to use the NVMe FLUSH command to flush the volatile write
   cache.

3.  Security Considerations

   Since no protocol changes are proposed here, no security
   considerations apply.

4.  IANA Considerations

   The document does not require any actions by IANA.

5.  Normative References

   [NVME]     NVM Express, Inc., "NVM Express Revision 1.3", May 2017.

   [NVME-STLR]
              NVM Express, Inc., "NVM Express: SCSI Translation
              Reference Revision 1.5", June 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [RFC8154]  Hellwig, C., "Parallel NFS (pNFS) Small Computer System
              Interface (SCSI) Layout", May 2017.

   [SBC3]     INCITS Technical Committee T10, "SCSI Block Commands-3",
              ANSI INCITS INCITS 514-2014, ISO/IEC 14776-323, 2014.

   [SPC4]     INCITS Technical Committee T10, "SCSI Primary Commands-4",
              ANSI INCITS 513-2015, 2015.

Author's Address

   Christoph Hellwig

   Email: hch@lst.de














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